Solution-processable electronic materials have attracted attention, because they may have the potential to permit the low-cost, scalable fabrication of lightweight, flexible devices (see, e.g., Friend, R. H. et al. Nature 1999, 397, 121; and Shirasaki, Y. et al. Nat. Photon. 2013, 7, 13). Recently, earth-abundant organometal halide perovskites that can be solution processed have emerged as a new class of semiconductors for photovoltaic devices. They have the potential to offer one or more advantages, such as low temperature processing, tunable optical band gap, and favorable charge transport. These solution-processed perovskites have also shown promise in light emitting diodes (LEDs).
However, the performance of perovskite-based LEDs (PeLEDs) reported to date has not reached the level of performance typically associated with organic or quantum dot based LEDs that share similar device architecture and operating mechanisms (see, e.g., Shirasaki, Y. et al. Nat. Photon. 2013, 7, 13; and Yang, Y. et al. Nat. Photon. 2015, 9, 259). Effort has been made to optimize the device configurations and thin film morphology to improve the brightness and the quantum efficiency of PeLEDs. For example, interfacial engineering has been investigated to reduce the electron or hole injection barriers for efficient electroluminescence (EL) (Yu, J. C. et al. Adv. Mater. 2015, 27, 3492). Other devices that have been fabricated include an ionic conductive poly(ethylene oxide) that was used to form uniform perovskite/polymer composite thin films as emitting layers (Li, J. et al. Adv. Mater. 2015, 27, 5196).
It has been observed that the film quality and/or optical properties of bulk perovskite films can depend heavily on the choice of substrate (Wang, J. et al. Adv. Mate. 2015, 27, 2311).
Provided that bulk perovskite thin films often suffer from poor morphology and/or low luminescent quantum yield, researchers have attempted embedding highly luminescent perovskite nanocrystals in a pinhole-free matrix of dielectric polymer to generate better LED performance (Li G. et al. Nano Lett. 2015, 15, 2640).
Although luminescent colloid organometal halide perovskite nanoparticles with high quantum yields have been reported, no efficient PeLEDs that include perovskite nanoparticles have been demonstrated (see, e.g., Zhang, F. et al. ACS Nano 2015, 9, 4533; Jang, D. M. et al. Nano Lett. 2015, 15, 5191; Tyagi, P. et al. J. Phys. Chem. Lett. 2015, 6, 1911; Schmidt, L. C. et al. J. Am. Chem. Soc. 2014, 136, 850; and Noel, N. K. et al. ACS Nano 2014, 8, 9815).
Therefore, there remains a need for nanoscale perovskites and PeLEDs that include nanoscale perovskite materials that offer one or more of the following advantages: efficiency, bright luminescence, high charge carrier mobility, broadband color tunability, color purity with narrow-band emission, and/or morphological and/or optoelectronic properties that are not substantially influenced by the surface properties of substrates. Facile methods for producing nanoscale perovskite materials also are desired, including methods that do not require the preparation of amine halide salts and/or the use of inert conditions when fabricating devices or handling the nanoscale perovskites.